In a radio communication system, particularly in a portable radio communication system, which uses a battery as a power supply, communications are disabled when the battery is exhausted. In order to allow the radio communication system to operate for a longer period of time even when the battery is used, it is demanded to provide a technique of reducing the power consumption by performing an intermittent operation in which the radio communication system operates only when communications are made and stops its operation in the other periods of time (for example, see JP H07-322364-A2).
FIG. 7 is a circuit block diagram of a remote control device for residence facility equipment, which serves as a radio communication system having an environment observation function. The remote control device includes a reception circuit 110, a transmission circuit 120, a transmission and reception control means 130, a battery 150, a constant voltage circuit 151, a reception-section power source control circuit 160, a transmission-section power source control circuit 170, an operation section 180, and a display section 190. The reception circuit 110 is composed of a first circuit group 117 that includes a VCO circuit 115 and a PLL circuit 116 and a second circuit group 118 that includes an RF circuit 111, a mixer circuit 112, an IF circuit 113, and a DET circuit 114.
The circuits included in the first circuit group 117 need a certain amount of time until their functions become effective after power is supplied, whereas the circuits included in the second circuit group 118 need a shorter period of time until their functions become effective after power is supplied. In other words, the circuits are grouped into the first circuit group 117 and the second circuit group 118 depending on time for which the circuit functions need to be effective. The reception-section power source control circuit 160 controls power supply timing to reduce power consumed for signal waiting in the respective circuit groups.
However, the above-mentioned conventional radio communication system has a problem in that the power consumption is not efficiently reduced because no consideration is given to circuits, such as the transmission and reception control means 130, which do not need to be operated while the transmission circuit and the reception circuit are being operated.
In the above-mentioned conventional radio communication system which includes a plurality of circuit blocks, a reduction in power consumption of each of the plurality of circuit blocks is not realized.
Specifically, in a wireless sensor network system serving as a radio communication system having a meter reading system for gas, water, and electricity or a radio communication system having an observation system for natural environments that include air temperature, room temperature, humidity, and illuminance, during transmission and reception of radio wave signals in the radio communication system, a circuit block of the meter reading system or the observation system does not need to be operated. Further, in the meter reading system or the observation system, during meter reading or observation, a circuit block having a function of transmitting and receiving radio wave signals does not need to be operated.
The present invention has been made to solve the above-mentioned problem, and therefore, it is an object of the present invention to provide a radio communication system having a meter reading system or an observation system, which does not need to replace a battery frequently by extending the lifetime of a battery of a wireless sensor network system.